System and method for sperm sorting

ABSTRACT

A system and method for sorting sperm is provided. The system includes a housing and a microfluidic system supported by the housing. The system also includes an inlet providing access to the microfluidic system to deliver sperm to the microfluidic system and an outlet providing access to the microfluidic system to harvest sorted sperm from the microfluidic system. The microfluidic system provides a flow path for sperm from the inlet to the outlet and includes at least one channel extending from the inlet to the outlet to allow sperm delivered to the microfluidic system through the inlet to progress along the flow path toward the outlet. The microfluidic system also includes a filter including a first plurality of micropores arranged in the flow path between the inlet and the outlet to cause sperm traveling along the flow path to move against through the filter and gravity to reach the outlet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application represents the national stage entry of PCT International Application No. PCT/US2014/066405 filed Nov. 19, 2014, which claims priority to U.S. Provisional Application Ser. No. 61/906,740, filed Nov. 20,2013, both of which are incorporated herein by reference for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

N/A

BACKGROUND OF THE INVENTION

The present invention relates generally to systems and methods for sperm sorting.

According to estimates, there are more than 70 million infertile couples worldwide. Approximately 1 in every 4 infertile couples seek clinical treatment, where, according to sources, male factor may account for about 50 percent of the infertility cases. Assisted reproductive technology (ARTs), such as in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), and intrauterine insemination (IUD, are generally utilized in reproductive clinics to treat infertile couples. With an increasing rate of male infertility due to environmental and physiological conditions, there is an ever growing need for the use of ARTs in reproductive clinics. Isolation of the most motile and morphologically normal sperm is an integral process to commonly used IVF/ICSI procedures. Selection of healthy sperm from unprocessed semen (stock sperm) is crucial as it requires selecting sperm that is not only highly motile, but also has a normal morphology, mature nuclei, and lesser reactive oxygen species (ROS) production. Although current IVF/ICSI procedures results in successful pregnancy approximately 50 percent of the time, the output can be greatly compromised if the sperm being selected are abnormal.

Currently, the more commonly-known ART techniques use centrifugation based sperm swim-up, density gradient separation methods, and microfluidic based methods with/without the use of chemotaxis to sort sperm. These techniques have potential drawbacks and limitations in their use for procedures as delicate as IVF/ICSI. It is worth noting that the centrifugation based sperm sorting techniques, such as swim-up, compromise on sperm quality during the repetitive centrifugation steps. Quality of a sperm sample is degraded during swim-up technique due to ROS generation. ROS exposure can greatly harm the DNA of seemingly motile and healthy sperm. Furthermore, the centrifugation-based sperm sorting techniques are labor intensive, and outcome can vary from technician to technician.

Sperm sorting technologies based on microfluidics have an advantage because they can precisely handle small volume of sperm samples. On the other hand, microfluidic-based sperm sorting devices have very low throughput and can only process small semen volumes, such as 2 μl-50 μl, which limits their application to reproductive clinics, where normal sperm sample can have volume of 1.5 ml.

In a clinical ICSI procedure, an embryologist will have on average 20 oocytes that can be handled in four petri dishes, and will need 20 sperm. The embryologist would like to choose these 20 sperm in an oligospermic sample among a few hundred sperm. Such scenario would require real-time monitoring of individual sperm and collection from outlet when 20 sperm reach the outlet, which is not attainable using current clinical or microfluidic technologies. In a second procedure, where an embryologist is handling healthy samples, in vitro fertilization is performed using 0.5 million healthy sperm suspended in a 5-20 μl suspension to be introduced to an oocyte. However, current sorting systems, such as described above, do not provide the throughput needed to meet these criteria.

Traditionally, optical microscopes have been used to image sperm for computer assisted sperm analysis (CASA) and manual identification of sperm motility for ARTs. This classical approach has limitations in tracking a large number of sperm simultaneously due to its small field of view (FOV). In addition, sperm tracking and motility analyses are performed after sorting. Currently no system exists that can sort and analyze sperm simultaneously.

It would therefore be desirable to provide a system and method for processing, including as sorting, sperm without damaging the sperm or subjecting the sperm to potentially-damaging conditions. Furthermore, it would be desirable to provide a system and method that can analyze sperm, but is efficient and able to scale.

SUMMARY OF THE INVENTION

The present invention overcomes the aforementioned drawbacks by providing a system and method that integrates micro- and macro-fluidics to sort sperm in a manner that allows efficient selection of sperm that are favorably suited to fertilization. In particular, the present invention recognizes that sperm suited to fertilization is most desirable and can be selected or sorted using a system presents and environment that is akin to that presented in the fertilization process. In this regard, a system is provided where macro reservoirs are connected by micropores to approximate the female genital track. A system and method is provide whereby the most motile, morphologically normal, mature, and functional sperm pass selectively through the micropores against gravity leaving behind dead or less functional sperm. The present invention is a chemical-free, centrifugation-free, and flow-free technology, where functional sperm are isolated from unprocessed semen sample with high retrieval rate.

In accordance with one aspect of the invention, a system for sorting sperm is provided that includes a housing and a microfluidic system supported by the housing. The system also includes an inlet providing access to the microfluidic system to deliver sperm to the microfluidic system and an outlet providing access to the microfluidic system to harvest sorted sperm from the microfluidic system. The microfluidic system provides a flow path for sperm from the inlet to the outlet and includes at least one channel extending from the inlet to the outlet to allow sperm delivered to the microfluidic system through the inlet to progress along the flow path toward the outlet. The microfluidic system also includes a filter including a plurality of micropores and arranged in the flow path between the inlet and the outlet to cause sperm traveling along the flow path to move against the filter and gravity to reach the outlet.

In accordance with another aspect of the invention, a method for sorting sperm is disclosed that includes delivering a sample of sperm to an inlet connected to a microfluidic system and allowing sperm in the sample of sperm to traverse a flow path through the microfluidic system toward an outlet providing access to the microfluidic system to harvest sorted sperm from the microfluidic system. The method also includes filtering the sperm prior to reaching the outlet using a filter having a plurality of micropores and gravity to restrict movement of the sperm through the filter. The method further includes harvesting sperm passing to the outlet after passing through the filter and overcoming gravity.

The foregoing and other aspects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a sperm sorting system in accordance with the present invention.

FIG. 1B is a cross-sectional view of the system of FIG. 1A.

FIG. 1C is a schematic view of multichannel system with a collection chamber to concentrate the sorted sperm.

FIG. 1D is a schematic view of multi-well system with multiple channels connecting the inlet and collection or concentration chamber chamber.

FIG. 2A is an exploded, cross-sectional view of a sperm sorting and imaging system in accordance with the present invention.

FIG. 2B is a detailed, perspective view of a microfluidic system of FIG. 1A or 2A.

FIG. 2C is a schematic view of a multi-channel microfluidic system in accordance with the present invention.

FIG. 2D is a cross-sectional view of overall system for sperm sorting and imaging system in accordance with the present invention.

FIG. 3 is a perspective view of a prototype system for sorting sperm in accordance with the present invention.

FIG. 4 is a series of images of sperm acquired using the present invention.

FIG. 5A is graph illustrating motility of human sperm isolated using different pore diameter filters and retrieved at different time points

FIG. 5B is a graph illustrating retrieval rate of sorted sperm using different chips.

FIGS. 6A, 6B, and 6C are graphs illustrating curvilinear velocity (VCL), straight line velocity (VSL), and average path velocity (VAP) of stock and sorted sperm using 3, 5, and 8 μm MMSS chips, respectively.

FIG. 7 is a graph showing normal morphology (%) for stock and sorted sperm.

FIG. 8 is a graph showing mature sperm percentage calculated for stock and sorted sperm.

FIG. 9A is a graph showing sperm sorted using 3, 5, and 8 μm filter devices showed significantly lesser ROS generation compared to swim-up and washing methods.

FIGS. 9B through 9G are reactive oxygen species (ROS) generation graphs for (B) Semen sample, (C) Washed sperm, (D) Sperm sorted using swim-up method (ROS region is highlighted by circle), (E) Sperm sorted using 3 μm MMSS chip, (F) Sperm sorted using 5 μm MMSS chip, and (G) Sperm sorted using 8 μm MMSS chip.

FIG. 10A is a graph showing sperm sorted using 5 and 8 μm MMSS chips showed significantly lesser DNA fragmentation compared to swim-up and unsorted semen sample.

FIGS. 10B through 10F are DNA fragmentation scatter plots for (B) Semen sample, (C) Sperm sorted using swim-up method, (D) Sperm sorted using 3 μm MMSS chip, (E) Sperm sorted using 5 μm MMSS chip, and (F) Sperm sorted using 8 μm MMSS chip.

FIG. 11 is a flow chart setting forth an example of some steps in accordance with the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The present invention recognizes that the vaginal mucus becomes watery and forms tiny microchannels that help guide sperm through to the egg. The present invention recognizes exhaustion as a mechanism for sorting sperm and has been experimentally and theoretically demonstrated to leverage exhaustion to sort healthy sperm using coarse-grained multi-scale simulation. Specifically, the present invention provides a macro-micro fluidic sperm sorting (MMSS) system to efficiently, reliably, and successfully sort sperm. As will be described, healthy motile sperm is fully collected at the outlets post-sorting. This system improves the efficiency of sperm selection process with minimal perturbation, thereby controlling against DNA fragmentation, accumulation of debris, and generation of ROS.

In addition, the present invention can simultaneously sort, monitor, and evaluate sperm. Specifically, the present system enables evaluation of each sperm individually, for example, based on velocity response, using a wide field-of-view (FOV) lensless imaging technology. The system provides a microchip-based, wide-FOV, lensless technology utilizing shadow imaging. Additionally, the present invention can be used to harvest morphometrical information, which is a reliable indicator of male fertility.

Referring to FIG. 1A, a sperm sorting system 10 is illustrated. The system 10 may be a polydimethylsiloxane-(PDMS) based, polymethylmethacrylate-(PMMA) based, or other microfluidic system. The system 10 includes a housing 12 having an inlet 14 and a collection chamber 16 having a filter 18 arranged therein. The filter 18 may be a polycarbonate filter or other filter having suitable materials properties, such as pore or passage size, as will be described. Referring to FIG. 1B, the inlet 14 and collection chamber 16 are connected through a passage or flow path 20 extending along a microfluidic chip 22. As will be described, the microfluidic chip 22 may include a microchip that may be disposable and that handles unprocessed semen samples (either fresh or frozen, processed or raw), for example of 10 μl-3 ml, and sorts sperm rapidly, such as in less than 30 minutes, without the need for complex instrumentation or trained operators.

The flow path 20 extends from the inlet 14 to the collection chamber 16. At the collection chamber 16 a first or bottom chamber 24 is located proximate to the microfluidic chip 22 and a second or top chamber 26 is located distally with respect to the microfluidic chip 22, above the first or bottom chamber 24. As will be described, the first chamber 24 is designed to collect the semen of a sample, whether fresh or frozen, processed or raw, presented to the inlet 14 and the second chamber 26 is designed to filter the motile sperms.

Referring to FIG. 1C, the system described above with respect to FIG. 1B may be modified to include an additional collection or “concentration” chamber 25 that is connected to the top chamber by a fluid connection 27. That is, in this regard, the sperm may be concentrated in the collection chamber 25 to facilitate easier harvesting.

In another configuration, as illustrated in FIG. 1D, the collection chamber 25 may be connected through a plurality of channels 28 each having an inlet 29 opposite the concentration chamber 25. In this regard, sperm from multiple flow paths 20 of FIG. 1C or from multiple collection chambers 16 may be delivered to a common concentration chamber 25. Such variations on the above-described design can be used to facilitate the use of multiple filters and multiple channels to handle even larger volumes or for higher throughput applications.

Referring to FIG. 2A, an exploded view of one optional configuration of the system 10 that includes an integrated imaging system is illustrated. The imaging system may form a lensless, wide-FOV imaging platform. In this view, components of the integrated imaging system, such as a light 30, an imaging sensor 31, and a glass protection layer 32 combined with the above-described system 10. In function, the light 30 illuminates sperm 34 introduced to the microfluidic chip 22 through the inlet 14. The illuminated sperm 34 can be imaged by the imaging sensor 31, which may be a charge-coupled device (CCD), complementary metal-oxide-semiconductor (CMOS), or other imaging device. More, specifically, referring to FIG. 2B, in function, sperm and semen 34 may be introduced into the outlet 14 using, for example, a pipette 36. The sperm traverse across a media 38 along the microfluidic chip 22, which may include the aforementioned glass 32, as well as a PMMA or other material layer 40, with a double-sided adhesive (DSA) layer 42 arranged there between to affix the glass 32 and PMMA layer 40 together. Ultimately, the sperm 34 traverse the microfluidic chip 22 to the outlet 16, where a mineral oil 44 may be found. Specifically, a thin layer of sterile, embryo-tested mineral oil may be placed on top of the media 38 in the inlet 14 and outlet 16 to avoid medium evaporation.

As illustrated, different channel lengths may be used or selected for effective sperm sorting. Furthermore, referring to FIG. 2C, a multichannel design may be utilized where the inlet 14 and collection chamber 16 are connected by multiple channels 46. As illustrated, a PBS collection buffer 48 may also be included, for example, to use in washings. Furthermore, the chip substrate housing the channels may be disposable.

Referring to FIGS. 2A and 2B, if included, lensless imaging can be used to record the shadow image of each individual sperm 34 onto an optoelectronic sensor array plane 31. This system 10 targets detecting/counting cells or monitoring in real-time the dynamic location of hundreds of thousands of individual cells on-chip over an ultra-wide FOV, for example, an FOV that is a few centimeters by a few centimeters. This technology provides these features with reduced complexity and ease of miniaturization.

One particular example of the system 10 including the imaging capabilities is illustrated in FIG. 2D. A standard microscope cannot monitor a whole microfluidic sorting chip and analyze sperm in real time. This challenge can be addressed by integrating lensless imaging with microchannels providing parallel on-chip monitoring and counting of sperm. The design permits miniaturization of this technology to make it suitable for an embryology/clinical lab and point-of-care settings.

The system 10, in the example in FIG. 2D, includes the light source 30 that is directed through an aperture 50 in the housing 12, such as a 50 μm aperture, to focus monochromatic light 52 toward a the microfluidic chip 22, across which the sperm 34 traverse, as described above. The system 10 may be coupled with a computer system 54 connected through a data connection 56, which may be wired or wireless, and a rechargeable battery or other power source 58 coupled through a power connection 60 to provide operational power for the imaging capabilities.

In one configuration, a combination of polymethyl-methacrylate (PMMA) of 1.5 mm thickness and double-sided adhesive (DSA) film of 50 μm thickness could be used to create microchannels. The DSA film can be cut to create microchannels of different lengths ranging from 5 mm to 40 mm using a laser cutter. Inlet and outlet ports extend through the PMMA with a diameter of 0.65 mm and 2 mm, respectively. The DSA film is then placed directly onto the PMMA in effect joining the two. A glass slide is placed onto the other side of the DSA film, such that the height of the channel is determined by the adhesive layer thickness. The larger outlet size is particularly designed to extract sorted sperm out of the channel easily accessible by a pipette. The distance between inlet and outlet determined the channel length. The length of the channel is defined as the distance between inlet and outlet.

To increase percentage of motile cells at the outlet and for high volume processing, a polycarbonate filter can be integrated into these microchips. This filter-based device can be designed using 3 mm thick PMMA cut to an area of 50 mm by 30 mm and another cut to an area of 30 mm by 30 mm. Cylinders of 20 mm diameter can be cut into both PMMA components and align vertically onto one another using 150 μm DSA. A 0.6 mm semen injection inlet is also cut into the larger device component at a 10 mm distance. The system can be assembled using a whatman nucleopore filter located between the two PMMA components.

Referring to FIGS. 1A through 2D, the system 10 can be used in large-scale semen processing. To do so, the sperm 34 is introduced through the inlet 14 to be place in the microfluidic chip 22. During this movement, the sperm 34 can be imaged using the light 30 and imaging sensor 31. The sperm 34 move toward the outlet 16. This outlet/collection chamber presents two chambers 24, 26. The first chamber 24 includes a filter presenting micropores and the second chamber 26 includes another filter including micropores. In this regard, the system 10 presents macro reservoirs 14, 16 connected by micropores to approximate the female genital track. Therein, the sperm 34 move collectively, influenced by each other, such as would naturally occur, along the medium 38 toward the outlet 16. The most motile, morphologically normal, mature, and functional sperm pass selectively through the micropores against gravity leaving behind dead or less functional sperm in the first chamber 24. That is, the sperm head is of spherical shape and has size of about 3 μm×4.5 μm. Sperm tails are about 45-50 μm long. If a filter having micropores of diameter larger than sperm head is placed in the first and second chambers 24, 26, only sperm that are motile can make their way through the micropores, whereas dead, dying, or damaged sperm cannot pass through the micropores because of their long tails. Instead, these dead, dying, and/or damaged sperm succumb to gravity and remain in the first chamber 24.

Thus, a microchip-based system is provided that is designed such that it does not require any centrifugation steps to retrieve healthy, motile, and morphologically normal sperm with minimal ROS generation. The device design makes sperm sorting procedure less labor intensive and inexpensive. The system incorporates utilizes exhaustion in space-constrained channels as a mechanism for sperm sorting. The system can isolate motile and morphologically normal sperm without any centrifugation step. Thus, a current coarse-grained model of sperm motility is used to model filter-based microfluidic devices in three dimensions, incorporating effects of cooperatively rising from hydrodynamic interactions between sperm, with channel walls, and with the filter surfaces and holes. This model allows the design of device parameters such as micropore size and incubation times.

The design and operation of the above-described system can be further appreciated from the following discussion of one example of a system, configuration for such system, and testing results of such system. This is but one example and is non-limiting in nature to the variety of configurations, designs, and operations that may be employed and fall within the scope of the present invention.

Example

Assembly of MMSS Chip

The poly (methyl methacrylate) (PMMA, 3 mm thick; McMaster Carr, Atlanta, Ga.) and double side adhesive (DSA, 120 μm thick, St. Paul, Minn.) were cut using a laser cutter (Versa Laser™, Scottsdale, Ariz.). The design for the chip was generated on Coral Draw4 and implemented onto USLE Engrave software for cutting. Primary components of the MMSS chip included one 3 mm PMMA cut to an area of 50 mm×30 mm (bottom chamber) and another cut to an area of 30 mm×30 mm (top chamber). A 0.6 mm injection point was also cut into the bottom PMMA sheet at a 5 mm distance from the chambers. Cylinders of 20 mm diameter were cut into both PMMA components. The bottom PMMA chamber was first attached to glass slide using DSA. Top PMMA chamber was aligned and attached with bottom chamber using DSA. The Nuclepore™ track-etched polycarbonate membrane filters (Whatman Ltd, 25 mm diameter, 3 μm, 5 μm, 8 μm) were sandwiched between two PMMA chambers during chip assembly. Thus, it was considered that at least 1 μm and less than 10 μm may be a range of advantageous pore sizes. A perspective view of the assembled chip is shown in FIG. 3.

Sperm Sorting using MMSS Chip

Thawed, unprocessed semen sample (stock sperm) was injected into the inlet of MMSS chip until it filled the first/bottom chamber. The first/bottom chamber was designed to hold up to 560 μl of the semen sample. In another set of experiments, the stock semen sample was diluted 4 times with 1 percent bovine serum albumin (BSA) in human tubal fluid (HTF) before injection into MMSS chip. Following injection, the first/upper chamber was topped off with 560 μl of 1 percent BSA in HTF. Chips were then stored at 37 degrees C. in incubator for 15, 30, 45, and 60 min intervals before fluid from top chamber was collected into eppendorph tubes for analysis.

Concentration and Motility Analysis

A standard Makler Haemocytometer was used to analyze the sperm samples for concentration and motility using optical microscope. Briefly, 1 μl of sperm sample was pipetted onto Makler Haemocytometer and covered with cover-lid provided with Haemocytometer. Sperm were counted by personnel familiar with method using a click-counter for at least three times. The sperm that were moving forward were considered motile.

Viability Analysis

The sperm samples were analyzed for viability using LIVE/DEAD® Sperm Viability Kit (L-7011, Molecular Probes®). SYBR 14 dye was used to stain live whereas Propidium Iodide (PI) was used to stain dead sperm. Samples were stained according to manufacturer's protocol. Briefly, first SYBR 14 dye was added into sperm sample to the final concentration of 100 nM. The sample was incubated for 5 min at 37° C. To stain the dead sperm, PI dye was added to the sample to the final concentration of 10 μM and allowed to incubate for 5 additional min. The sperm samples were smeared on a glass cover slip and imaged using fluorescent microscope Zeiss Axio Observer.Z1. Green and red emission filters were used for SYBR 14 and PI, respectively.

Velocity Measurement

Sperm samples were analyzed using the method described by WHO laboratory manual for sperm analysis. Briefly, sperm was retrieved from the MMSS chips (3 μm, 5 μm, 8 μm) after 30 min. Slides were prepared by putting 6 μl of sperm sample onto a glass slide and covered by using a 18×18 mm cover slip to give the sample a depth of 20.7 μmm. To avoid drying up of samples, slides were made periodically, not simultaneously. Each slide was analyzed under 20× (Carl Zeiss) using light microscopy with live images of the sample being projected onto a computer monitor. Using a video capturing software (Snagit, TechSmith), movement of sperm samples were captured at random locations for 5 secs. Videos were converted to image sequences using VideotoJpeg software at 100 fps. The image sequence was input into ImageJ (National Institute of Health, http://rsbweb.nih.gov/ij/) for analysis using the CASA plugin to monitor sperm velocity parameters, i.e. straight line velocity (VSL), curvilinear velocity (VCL), and average path velocity (VAP).

Sperm Morphology Assessment

Recovered sperm suspension from 5 μm, and 8 μm MMSS chips were collected after 30 mins. Sperm retrieved from 3 μm MMSS chip were not analyzed for sperm morphology, as sperm concentration is too low for morphology analysis. A 10 μL sperm suspension was then taken and placed on a clean and sterile microscope slide and feathered smears were prepared. Smears were air dried and prepared for fixation. A Spermac staining protocol similar to the one provided by FertiPro was followed to stain sperm for morphology assessments. Briefly, dried smears were submerged into Spermac fixative solution for at least 5 min and then rinsed with DI water. Stain A was pipetted at one edge of the slides and allowed to flow over the smear. Slides were then placed on a flat surface and allowed to soak with stain for 1 min. The slides were then rinsed with DI water twice. Next, stain B was applied similarly to Stain A and allowed to penetrate sperm for 1 min. This was followed by a single rinse with DI water. Finally, stain C was pipetted over the smear and allowed to sit for 1 min before rinsing with DI water. At this point, at least 100 sperm were imaged using oil immersion and 100× objective (N (no. of repeats)=3). The sperm was considered morphologically normal if it falls within WHO morphology criteria (Head: spherical head; acrosome covering 40-70% of head area; head length 3.7-4.7 μm; head width 2.5-3.2 μm; length-to-width ratio 1.3-1.8; no more than 2 small vacuoles; post-acrosome region should not contain any vacuole. Midpiece: no residual cytoplasm in midpiece; length of midpiece should be approximately same as head length; no broken neck. Principal piece: no sharp angles or bends indicative of tail break; thinner than midpiece, length of principal piece should be approximately 10 times the head length).

Sperm Maturity Assessment

Recovered sperm suspension from 5, and 8 μm MMSS chips were collected after 30 mins. Sperm retrieved from 3 μm MMSS chip were not analyzed for nuclear maturity, as sperm concentration is too low for this analysis. Dried smears were fixed with the Spermac fixative solution for 5 min and subsequently rinsed with DI water. A 5% aniline blue in 4% acetic acid solution was prepared and was poured over smears. Smears were soaked for 5 min in staining solution and then rinsed with DI water. At least 100 sperm were assessed using oil immersion 100× objective (N (no. of repeats)=3). Sperm heads that stained dark blue were declared immature, while those that remained unstained were considered mature.

ROS Detection

Sperm Washing:

1 ml of semen was removed from a cryopreservation tank and thawed for 15 min in a 37° C. warm bath. Washed semen sample was prepared by adding 9 ml of HTF+1% BSA media to 1 ml of semen, centrifuging for 500×g for 5 min and removing supernatant while leaving sperm pellet at the bottom of tube. This procedure was repeated three times. HTF media was added to sperm pellet and samples were stained with ROS studies.

Swim-Up Method:

1 ml of semen was removed from a cryopreservation tank and thawed for 15 mins in a 37 desires C. warm bath. The semen was diluted with 9 mL of HTF+1% BSA. The diluted sperm suspension was then centrifuged at 500×g for 5 mins. Following, the supernatant was removed and disposed. The remaining pellet was washed again by centrifuging sample at 500×g for 5 min. The supernatant was removed and disposed again. Finally, 500 μL of medium was added along the side wall of centrifuge tube while avoiding the disruption of the pellet. The sample was then placed in the incubator and motile sperm were allowed to swim up out of pellet for 30 min. The motile sperm were collected by leaving pellet behind. MMSS chips were incubated for a 30 mins period and sperm suspension was recovered for ROS studies.

Staining for ROS Detection:

ROS generation was examined by using flow cytometry in conjunction with two fluorescent dyes, dyhydroethidium (DHE) and SYTOX green. DHE reacts with the superoxide anion which produces two fluorochromes which bind to sperm DNA and produces a red fluorescence. While SYTOX green is indicative of cell viability, it produces a green fluorescence when the cell is dead. For this experiment, four control samples were prepared in which all consisted of 200 μL of recovered sperm suspension mixed with 20 μL of hydrogen peroxide. This was followed by an incubation at 37 degrees C. for 30 mins. The dyes were added to the samples; no dye for negative control, DHE at 5 μM was added to the second sample, SYTOX green at 50 nM was added to the third sample, and the fourth sample contained both DHE and SYTOX at 5 μM and 50 nM respectively. Dyes were incubated for 15 mins and then transferred to the flow cytometer for measurement 15 min prior to test samples. FACSCalibur flow cytometer (Becton Becton Dickinson, San Jose, Calif.) was used during experiments. Argon laser excitation at 488 nm was coupled with emission measurements using 530/30 band pass (green) and 585/42 band pass (red) filters for FL1 and FL2, respectively. Non-sperm events were gated out, and at least 10,000 cells were examined. For test samples, 500 μL sample from thawed semen, the swim up suspension, 3, 5, and 8 μm filter pore size microchips were collected. DHE and SYTOX at 5 μM and 50 nM respectively were added to each sample and allowed to incubate for 15 min. Samples were taken to the flow cytometer for measurement.

DNA Fragmentation

TUNEL assay kit (In Situ Cell Death Detection Kit, Fluorescein by Roche Applied Science) was used to quantify DNA fragmentation for raw semen, swim-up, and retrieved sperm population from microchip devices with filters of 3, 5 and 8 μm pore size. All these samples were attained as previously mentioned in ROS Detection section. Initially, all the sperm suspensions were washed twice by centrifuging at 500×g for 5 min with PBS and 1% BSA. Once washed, the concentrations of sperm cells were adjusted to 2×10⁶ cells/ml. Sperm suspensions were then fixed with 4% paraformaldehyde in PBS (200 μL for every 100 μL of cell suspension) for 30 min at room temperature. Sperm cells were washed twice at 500×g for 6 min with PBS and 1% BSA and permeabilized with 0.1% TritonX in 0.1% sodium citrate for 2 min in/on ice. Sperm were washed twice followed by 1 hour incubation at 37° C. with 5 μL of enzyme (TdT) solution and 45 μL of label (dUTP-Flourescein) solution. Similarly, a negative and positive control sample was prepared. However, prior to staining, the positive control was incubated with DNase for 40 min at 37° C. During staining, the negative control was only incubated with label solution (without enzyme solution). After staining, samples were washed twice with PBS and 1% BSA and resuspended in PBS (Muratori et al, 2000). Fluorescence emission of DNA fragmented cells were assessed with flow cytometer and detected by the FL-1 detector (521 nm). A total of 5000 events were acquired. Sperm population was gated out from data to eliminate any signal from debris. Experiments are repeated 6 times (N=6).

Results and Discussion

To develop a chemical-free and centrifugation-free, high-throughput, vertical sperm sorting device, the MMSS chips were fabricated and assembled as described above. Briefly, it is a two-chamber chip separated by polycarbonate filters of various diameters, such as, for example, 3, 5, 8 μm. The sperm sample was injected into the bottom chamber and sorted motile/healthy sperm were collected from the top retrieval chamber. The presence of the filters with, for example, uniform sized pores between two chambers was designed such that the most motile and healthy sperm could translocate through the filter pores. Scanning electron microscope (SEM) images of polycarbonate filters used for sperm sorting showed uniform pore diameters as shown in FIG. 4. SEM images of polycarbonate nuclepore track-etched membrane filters of different micropore diameters, i) 3 μm ii) 5 μm and iii) 8 μm. The scale bar is 10 μm. These images shows the comparative size of various filter pores and sperm.

The sperm head is of spherical shape and has size of about 3 μm×4.5 μm. Sperm tail is about 45-50 μm long. If a filter of diameter larger than sperm head is placed between this two-chamber chip, only sperm which are motile can make their way through the micropores whereas dead/dying sperm cannot pass through the micropores because of their long tails.

Sperm Motility and Retrieval Rate

To investigate the motility of the sorted sperm, we analyzed the sperm collected from the top retrieval chamber of all three MMSS chips (3, 5, and 8 μm diameter filter chips). Results showed that the sperm sorted with MMSS chips showed significantly higher motility as compared to stock sperm sample, such as illustrated in FIG. 5A. Specifically, the 3, 5, and 8 μm filter chips showed sperm motility of greater-than-or-equal-to 95 percent ±10, greater-than-or-equal-to 90.4 percent ±1.8, greater-than-or-equal-to 85.9 percent ±1.5, respectively, which was significantly higher than the stock sperm motility (39.8 percent ±1.9). We further investigated the effect of incubation time on sperm motility. Sperm were collected after 15, 30, 45 and 60 mins. We found that the motility of the retrieved sperm increased when sperm sample was collected after a longer period of time; motility in the case of 60 mins time point was highest whereas it was lowest for 15 minutes time points, such as illustrated in FIG. 5A. This increased motility is noticed in all three chips. When HTF+1 percent BSA was pipetted to the top chamber of the MMSS chip at the start of each experiment, slight turbulence would produce in the sperm sample due to mixing of the two liquids; stock sperm sample and HTF+1 percent BSA media. This turbulence in sperm sample is the possible reason for the lesser sperm motility at the start of the experiment (after 15 mins) as compared to latter time points (after 30, 45, and 60 mins). In addition, we calculated the sperm retrieval rate at various time points, that is, percentage (%) of healthy sperm retrieved out of stock sample. Retrieval rate is an important parameter for any sperm sorting device especially for the situation where sperm samples have low sperm count (oligospermic and azoospermic specimens). In the MMSS chip, the sperm retrieval rate was analyzed over a period of time; 15, 30, 45, and 60 min time points is illustrated in FIG. 5B. Sperm retrieval rate was maximum for samples collected after 30 mins time points (3.08 percent±0.42, 23.75 percent ±3.96, and 28.58 percent ±2.81 for 3, 5, and 8 μm MMSS chips, respectively). We call this 30 minutes time point as a saturation time point as sperm retrieval rate was reduced if the sample was incubated for more than 30 minutes, such as illustrated in FIG. 5B. We believe that some of the sperm might be travelling back through the filter into bottom chamber after 30 minutes.

Sperm Viability

Motile sperm are considered viable. To substantiate our finding that the sorted sperm are viable, we performed the live/dead staining for sorted sperm for 30 min time point. The viability of sorted sperm was significantly higher than stock sperm sample; 41.0 percent ±0.45 (stock sperm), 91.32 percent ±3.43 (3 μm MMSS chip), 89.83 percent ±5.82 (5 μm MMSS chip), 91.59 percent ±4.44 (3 μm MMSS chip).

Effect of Sample Dilution on Sperm Motility and Retrieval

To investigate the effect of sperm sample dilution on motility and retrieval rate, we diluted the stock sperm sample with HTF+1 percent BSA at the ratio of 1:4 before processing using MMSS chips. The motility of the sorted sperm was significantly higher than stock sperm sample at all 4 time points (15, 30, 45, and 60 mins); 45.8 percent ±1.5 (stock sperm), ≥95.0 percent ±5.0 (3 μm MMSS chip), ≥93.7 percent ±4.7 (5 μm MMSS chip), ≥90.7 percent ±2.5 (8 μm MMSS chip), whereas it was not different than if undiluted sperm sample was used, as shown in FIG. 5A. However, the sperm retrieval rate increased if diluted sperm sample is used instead of undiluted stock sperm, as shown in FIG. 5B. Maximum retrieval rate was found to be 52.68 percent ±4.97 for 8 μm chip after 30 minutes time point. In diluted sample, sperm has increased mean free path before hitting another sperm. This phenomena might has helped sperm in reaching and crossing the filter micropore faster. Secondly, the filter has fixed number of pores (<14 percent porosity). As lesser number of sperm were trying to cross the filter pores in diluted sample, it was more probable for each sperm to find an empty pore and translocate through it.

Sperm Velocity Analysis

Various sperm velocity parameters were analyzed, i.e. curvilinear velocity (VCL), straight line velocity (VSL), and average path velocity (VAP). A representative image of sperm track showing these velocity definitions is shown in Supplementary FIG. 3. The original sperm video from which FIG. 3 track is generated is given as Supplementary Movie 1. The sorted sperm using MMSS chips showed significantly higher sperm velocities than stock sperm sample, as illustrated in FIG. 6. Specifically, average sperm VCL was increased from 52.7±6.0 μm/sec (stock sperm) to 59.9±3.5 μm/sec, 75.3±3.1 μm/sec, and 75.6±4.5 μm/sec for 3, 5, and 8 μm MMSS chips, respectively, as illustrated in FIG. 6A. Average sperm VSL increased from 44.4±5.6 μm/sec (stock sperm) to 52.1±3.5 μm/sec, 63.4±3.5 μm/sec, and 64.1±3.9 μm/sec for 3, 5 and 8 μm chips, respectively, as illustrated in FIG. 6B. Average sperm VAP increased from 48.4±5.8 μm/sec (stock sperm) to 54.1±3.4 μm/sec, 68.0±2.9 μm/sec, and 67.5±4.1 μm/sec for 3, 5, and 8 μm chips, respectively, as illustrated in FIG. 6C. Higher sperm velocities indicate that the sorted sperm are healthier than stock sample. When we compared velocities among the sperm sorted using three different MMSS chips, it was noticed that sperm sorted using 5 and 8 μm MMSS chips gave higher VCL, VSL, and VAP velocities than 3 μm filter chip. This is probably due the fact that mostly immature motile sperm having head sizes smaller than 3 μm could pass through the 3 μm micropores. Only exception to this was the filter areas where two or more 3 μm pores were joined together to make up a larger pore.

Sperm Morphological Analysis

For morphological analysis, sperm were stained with Spermac Stain. Sperm were considered morphologically normal based on the strict criteria defined by WHO. Any sperm sample having >4 percent morphologically normal sperm is considered normal. We found that sperm sorted using 5 μm MMSS chips did not improve the sperm quality in term of overall morphology, though the sorted sperm were motile. Sperm sorted using 8 μm MMSS chips showed significantly improved morphology over stock and sperm sorted using 5 μm MMSS chip; 30.0 percent ±7.6 (8 μm MMSS chip), 17.0 percent ±3.2 (5 μm MMSS chip), and 17.6 percent ±0.5 (stock sperm).

Sperm Nuclear Maturity Analysis

Sperm were stained with aniline blue and analyzed for nuclear maturity. Aniline blue staining can discriminate the lysine-rich nuclei of immature sperm and arginine/cysteine-rich nuclei of mature sperm. The nuclei of immature sperm were stained with aniline blue and showed a color contrast between nuclei and acrosome. Representative images of sperm stained with aniline blue and their assessment criteria is shown in FIG. 7. Sperm sorted using 5 μm filter chip did not show any improvement over stock sperm in terms of nuclei maturity. Whereas, sperm sorted using 8 μm filter chip showed higher nuclear maturity than stock sperm sample, as shown in FIG. 8.; 40.8 percent ±5.1 (8 μm MMSS chip), 25 percent ±4.6 (5 μm MMSS chip), and 26.9 percent ±5.8 (stock sperm).

ROS Generation Analysis

Sorted sperm was analyzed for ROS generation. We have compared the ROS generation in the sperm after washing method, conventional swim-up method and MMSS chips. We found that sperm sorted by MMSS chips produced significantly lesser ROS than swim-up and washing method (FIG. 9). Sperm washing and swim-up method produced ROS in 10.1%±0.3% and 10.6%±1.1% of the sperm respectively, whereas sperm sorted using MMSS chips showed ROS production in only 0.8%±0.4% (3 μm MMSS chip), 0.7%±0.1% (5 μm MMSS chip) and 1.0%±0.1% (8 μm MMSS chip) of the sperm. Unsorted semen sample showed ROS generation in 1.8%±0.6% of the sperm, which clearly indicated that the increased generation of ROS in swim-up and washing methods came from centrifugation steps.

DNA Fragmentation Analysis

The analysis of sperm DNA fragmentation can differentiate fertile and infertile men, and sperm samples showing higher level of DNA fragmentation results lower fertilization rates in IVF/ICSI, impaired embryo progression and lower pregnancy rates. Sperm sorted using MMSS chips were analyzed for DNA fragmentation. DNA fragmentation (%) was 1.1%±0.3% (8 μm MMSS), 2.1%±0.7% (5 μm MMSS chip), 3.4%±0.8% (3 μm MMSS chip), 3.7%±1.2% (swim-up method), and 31.2%±1.2% (unsorted semen). The sorted sperm using 5 μm and 8 μm chips showed significantly lower DNA fragmentation (%) than unsorted semen sample and sperm sorted using swim-up method (FIG. 10).

Discussion

The ideal sperm sorting technique should (i) be rapid and cost-effective, (ii) be less labor intensive, (iii) process larger sperm volumes, (iv) have higher retrieval efficiency to isolate motile sperm from dead/non-motile sperm, (v) isolate sperm with higher velocity, (vi) isolate morphologically normal and mature sperm, (vii) reduce ROS generation and morphological damage by eliminating centrifugation steps, (viii) reduce the percentage of sperm DNA fragmentation. These parameters are generally desirable features for any sperm-sorting device and the system of the present invention offers a platform providing these features.

In the particular example provided herein, the total material cost to fabricate one chip is less than a dollar (50 cents for filter, <50 cents for PMMA and DSA). The MMSS chip rapidly (approximately 30 minutes) isolated motile sperm from non-motile ones with the higher retrieval rate (28.58 percent ±2.81 percent retrieval from stock sperm) than swim-up technique (<20 percent). The retrieval was further increased to 52.68 percent ±4.97 (8 μm filter) by using diluted sample. Although sperm dilution gave higher retrieval of healthy sperm, it reduced the actual stock sperm volume that could be processed at a time. The stock sperm may be desirably diluted before processing for (i) low volume ejaculates, and (ii) ejaculated with very low sperm count. MMSS chip design is highly scalable and can process large semen volumes by using larger filters (for example, 1.5 ml). Processing a large semen sample is needed to retrieve enough sperm for IVF procedures. Furthermore, high volume processing is very important for the samples having low sperm count or low sperm motility.

Sperm having higher velocity parameters can increase the ICSI fertilization rates. Sperm sorted by MMSS chip showed significantly enhanced velocity parameters (VCL, VSL and VAP) compared to stock sperm that clearly demonstrated that sorted sperm were of higher quality. Sperm morphology is another important indicator for a successful fertilization. Morphologically normal sperm increase the fertilization rate during IVF procedures. Sorting sperm using 8 μm MMSS chip improved sperm morphology by 1.7 folds, which is a significant improvement, as illustrated in FIG. 7. It is also interesting to note down the association of sperm motility and morphology. We found that morphologically normal sperm also showed better velocities, which demonstrated that these two functional parameters (sperm velocity and morphology) are associated.

Sperm nuclear maturity has shown an association with male infertility. Chromatin condensation as described by nuclear maturity is another predictor for IVF outcome. Sperm sorted using 8 μm MMSS chips showed significantly improved sperm maturity compared to stock sample, as illustrated in FIG. 8. We also looked into the ROS generation by human sperm. ROS generation is an important investigative tool to assess the sperm quality and its apoptosis status. There are many pathways and reasons leading to sperm ROS generation such as poor differentiation during spermiogenesis, poor chromatin compactness, exposure to heavy metals, heat or electromagnetic radiations, prolonged in vitro culture, and presence of sperm in the vicinity ROS generating cells. Conventional techniques utilizing centrifugation steps to sort healthy sperm is another reason for ROS generation as these techniques centrifuge sperm with ROS generating cells such as leukocytes. We found that sperm sorted using all three MMSS chips showed significantly low ROS generation compared to stock sperm.

DNA fragmentation is another very important indicator for male infertility. According to some reports, sperm DNA integrity can be considered as an independent marker for fertilization. Sperm sorted using MMSS chips showed a significant improvement in DNA fragmentation compared to unsorted semen sample, as shown in FIG. 10. Currently, sperm swim-up method is considered standard to sort sperm with lower DNA fragmentation. It is interesting to note here that the sperm sorted with 5 and 8 μm MMSS chips showed ever lower DNA fragmentation than swim-up method. We believe based on these functional assays that the sperm sorted using 8 μm MMSS chip are of better quality compared to conventional methods. The sorting of morphologically normal, mature, motile and functional sperm would potentially improve IVF/ICSI outcomes.

Referring now to FIG. 11, some example steps 100 in a process for sorting sperm are provided. The steps 100, beginning at process block 102, include receiving a sample of sperm to an inlet of a microfluidic system, such as described above. Thereafter, at process block 104 the sperm of the sample are allowed to traverse a flow path through the microfluidic system toward an outlet providing access to the microfluidic system for harvesting of sorted sperm from the microfluidic system. At process block 106, the sperm are subjected to a filter prior to reaching the outlet. As described, the filter has a plurality of micropores and is oriented restrict movement of the sperm through the filter using gravity. Thus, at process block 108, sorted sperm is provided at the outlet. The sorted sperm includes sperm passing to the outlet after passing through the filter and overcoming gravity.

Thus, the present disclosure provides system and methods for (i) development of a chemical free and flow free system to sort healthy sperm, analyze motility, speed and morphology, (ii) isolation of the sorted healthy sperm, and (iii) developing a better understanding of exhaustion and collective motion of sperm. This platform is an innovation beyond the existing clinical procedures such as the swim-up and microdrop techniques. It is also novel beyond the reported microfluidic based sperm sorting devices, as it uses a new ground-breaking knowledge of exhaustion in space-constrained channels for sorting and analyzing sperm. Given that clinical reproductive medicine has been a challenging field that is labor intensive, such an easy-to-use microchip can lead to improved selection of healthy sperm and decreased dependence on operator skills, facilitating repeatable, and reliable operational steps.

The present invention has been described in terms of one or more preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside from those expressly stated, are possible and within the scope of the invention. 

The invention claimed is:
 1. A system for sorting sperm comprising: a housing; a microfluidic system supported by the housing; an inlet providing access to the microfluidic system to deliver sperm to the microfluidic system; an outlet providing access to the microfluidic system to harvest sorted sperm from the microfluidic system; wherein the microfluidic system provides a flow path for sperm from the inlet to the outlet and comprises: a collection chamber at the outlet configured to pass motile sperms to the outlet and restrict non-motile sperm; at least one channel extending from the inlet to the collection chamber to allow sperm delivered to the microfluidic system through the inlet to progress along the flow path toward the outlet; a filter including a plurality of micropores and arranged in the collection chamber to cause sperm traveling along the flow path to move against the filter and gravity to reach the outlet; and a concentration chamber at the outlet in communication with the collection chamber and configured to concentrate the motile sperms to facilitate harvesting.
 2. The system of claim 1 wherein the plurality of micropores are sized to permit a head of the sperm to pass therethrough.
 3. The system of claim 1 wherein the plurality of micropores include micropores having a size of at least 1 μm.
 4. The system of claim 1 wherein the plurality of micropores include micropores having a size of less than 10 μm.
 5. The system of claim 1 wherein the plurality of micropores include micropores that are spherical in shape.
 6. The system of claim 1 wherein the filter includes a polycarbonate filter.
 7. The system of claim 1 wherein the collection chamber includes two sub-chambers.
 8. The system of claim 7 wherein the filter is arranged within one of the two sub-chambers.
 9. The system of claim 8 wherein a first of the two sub-chambers is configured to collect raw semen associated with the sperm and a second of the two sub-chambers is configured to pass motile sperms to the outlet and restrict non-motile sperm.
 10. The system of claim 1 further comprising an imaging system configured to image the sperm within the flow path.
 11. The system of claim 1 further comprising an imaging system including at least one light configured to illuminate the sperm within the flow path and an imaging sensor arranged proximate to the flow path to image the sperm.
 12. The system of claim 10 wherein the imaging sensor includes at least one of a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) imaging sensor.
 13. The system of claim 1 wherein the microfluidic system includes at least one of a polydimethylsiloxane-(PDMS) base or a polymethylmethacrylate-(PMMA) base.
 14. The system of claim 1 wherein the at least one channel includes a plurality of channels, each of the plurality of channels having different channel lengths. 